Star-forming systems, from sub-pc to super-Mpc scales, are scenes of powerful conflict. The protagonists include gravity and an array of other physical processes, many of which are produced by star formation itself. Both during their main sequence lifetimes and in their explosive deaths as supernovae, massive stars inject copious energy and momentum into their surroundings. This "feedback" energy and momentum heats, ionizes, and pushes on individual gas and dust fluid elements that absorb it. The feedback-driven expansion of overdense regions is crucial for limiting the action of gravity on a wide range of scales.

New observational evidence for the importance of star formation feedback, combined with recent advances in the computational tools needed for quantitative modeling, has sparked a fire among theorists. As feedback processes connect large and small scales, efforts to take on these questions seriously have led to increasing need for interactions between what were formerly quite distinct theoretical fields: the interstellar medium and galaxy formation.

This KITP program will connect diverse efforts on the physics of star formation feedback, bringing together Galactic and extragalactic communities to exchange ideas and techniques. Among the issues to be addressed by the program are:

• What types of feedback are at play, and what are their effects?
• What drives turbulence in galactic disks?
• What drives galactic outflows?
• How do various feedback processes (both in a galaxy and beyond its halo) affect star formation?
• How does feedback affect the IMF?
• How does feedback affect the distribution of metals?
• What are the observable effects of feedback, and how do we distinguish between different forms of feedback observationally?

In addition to taking on these and other science topics, a critical thrust of the program will be on evaluation and intercomparison of numerical methods for modeling feedback. Important issues include:

• What are the tradeoffs between speed and accuracy among new and established methods for solving the equations of radiation hydrodynamics?
• What approaches are most promising for treating cosmic rays and their interaction with the gas in galaxies?
• Can feedback effects be treated accurately using a subgrid model, in applications where limited resolution makes direct solution impossible?

To kick off the program, a conference will be held during the week of April 14 - 18, 2014. This forum will connect participants coming from different fields, introduce new observations from ALMA, Herschel, and large optical telescopes, review the state-of-the-art in numerical techniques, and highlight the most recent theoretical results and unsolved problems.